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Planetary News: Phoenix (2008)Phoenix Enters Safe ModeBy A.J.S. Rayl
The Phoenix Mars Lander entered safe mode late Tuesday in response to a low-power fault brought on by deteriorating weather conditions. While engineers anticipated that a fault might occur as a result of the diminishing power supply, the lander also unexpectedly switched to the "B" side of its redundant electronics and shut down one of its two batteries. In safe mode, Phoenix is programmed to stop non-critical activities and await further instructions from the mission team. Within hours of receiving information of the safing event, mission engineers at the Jet Propulsion Laboratory (JPL) in Pasadena and at Lockheed Martin in Denver, were able to send commands to restart battery charging. It is not likely that any energy was lost, according to an official announcement. Science activities will remain on hold for the next several days to allow Phoenix to recharge and conserve power. Attempts to resume normal operations will not take place before the weekend. "This is a precarious time for Phoenix," said Project Manager Barry Goldstein, of JPL. "We're in the bonus round of the extended mission, and we're aware that the end could come at any time. The engineering team is doing all it can to keep the spacecraft alive and collecting science, but at this point survivability depends on some factors out of our control, such as the weather and temperatures on Mars." Originally scheduled to last 90 days, Phoenix has completed 160 days or five months of exploration in the Martian arctic after landing in a region of permafrost on Mars's northern plains. Nicknamed Green Valley, the area is somewhat similar to permafrost regions in northern Canada.
Phoenix carved out its niche in Mars exploration history by being the world’s first spacecraft to land in the north polar regions and the first to reach out and touch the water-ice that turned out to be just below the surface where the University of Arizona's Bill Boynton and his Gamma Ray Spectrometer team on Mars Odyssey indicated it was some six and a half years ago. It is also the first spacecraft to see snow falling from Martian clouds. The mission objectives were to study the history of water in the Martian arctic, search for evidence of a habitable zone, and assess the biological potential of the ice-soil boundary and Phoenix succeeded in going where there was no planetary exploration trail and successfully left its path, as Peter Smith, the principal investigator, also of the University of Arizona, which oversaw the mission for NASA, said it would on landing night last May. Winter weather conditions are setting in at the landing site in the north polar region of Mars, with overnight temperatures falling to -141F (-96C), and daytime temperatures only reaching as high as -50F (-45C). These are the lowest temperatures Phoenix has experienced so far in the mission. A mild dust storm blowing through the area, along with water-ice clouds, further complicated the situation by reducing the amount of sunlight reaching the lander's solar arrays, thereby reducing the amount of power it could generate. The low temperatures, meanwhile, caused the lander's battery heaters to turn on Tuesday for the first time, creating another drain on precious power supplies.
The team’s ability to communicate with the spacecraft has not been impacted. Nevertheless, officials decided to cancel communication sessions Wednesday morning to allow Phoenix to conserve more power. The next communication pass was anticipated at 9:30 p.m. Pacific Daylight Time (PDT) last night. The mission announced plans earlier this week to turn off four heaters, one at a time, in an effort to preserve the fading power. The faults experienced late Tuesday, however, prompted engineers to command the lander to shut down two heaters instead of one as originally planned. One of those heaters warmed electronics for the robotic arm, robotic-arm camera, and Boynton's thermal and evolved-gas analyzer (TEGA), the instrument that bakes and ‘sniffs’ Martian soil to assess volatile ingredients. The second heater served the lander's pyrotechnic initiation unit, which hasn't been used since landing. Phoenix’s demise is inevitable. Until the Mars Exploration Rovers, Phoenix is a lander and cannot move to track the Sun and take in more photon fuel. So, as the planet’s northern hemisphere shifts from summer to autumn, the lander will generate less power simply because there will be fewer and fewer hours of sunlight reaching its solar panels.
By turning off selected heaters and conserving energy, the mission hopes Phoenix will be able to continue to use its camera and successfully sustain its meteorological instrument so it can operate as a weather station for a little while. "It could be a matter of days, or weeks, before the daily power generated by Phoenix is less than needed to operate the spacecraft," said JPL mission manager Chris Lewicki. "We have only a few options left to reduce the energy usage." There is a remote chance that Phoenix could be revived after winter passes, according to Goldstein. In reality, “the vehicle probably won’t survive the harsh winter and there will probably not be enough power on it to come back to life, so we’re not really hopeful that we can [revive it],” he said earlier. “But,” he added, “we’ll sure give it a try.” The Phoenix Mission is led by the University of Arizona, on behalf of NASA. Project management of the mission is by NASA's Jet Propulsion Laboratory and spacecraft development is by Lockheed Martin Space Systems, Denver.
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